During a recent dyno test of a new carburetor we were shocked to see our power numbers down about 50%. The first thing that came to mind was that perhaps the carburetor throttle blades were not opening completely. With the gas-pedal firmly planted to the floor I peered down the throat of the Holley 750 double-pumper. Sure enough the blades were cracked only 60% of the way. After some investigating the culprit was found to be the factory accelerator rod. It was not creating enough leverage to fully rotate the throttle arm on the carb. The stock accelerator rod is pre-bent to work with the factory carburetor. The resulting geometry however is less than ideal for most aftermarket carbs. We'd just been lucky that it had worked okay with past carburetors.

We're not sure why we put up with the stock rod for so many years. It never mounted securely to the carburetor arm, as it is intended to be used with a locking clip that only fits stock Motorcraft arms. Of all the money spent on aftermarket parts you'd think an ill fitting piece of rod would be quickly tossed for something new. Perhaps that's just the problem, new throttle linkages aren't a common sighting and what is available is hard on the wallet. Plus there is no guarantee the aftermarket stuff will fit. Our dyno guy had seen this problem many times before and ran over to the hardware store to round up the ingredients for a custom fit throttle linkage. Within 20 minutes, and less than $15 dollars, we had made up a trick looking adjustable linkage that functions smoothly, attaches securely, and ensures complete throttle opening. Here's how you can put one together:

The first step is to determine the overall length of the linkage. This length is the distance between the the 1/2" mounting hole in the throttle arm on the carb and the hole in the pedal "bell-crank". To calculate this length, place the accelerator pedal firmly to the floor. Completely open the throttle blades by hand and measure the distance from center of the 1/2" hole in the throttle arm to center of the attaching hole in the pedal arm.

Cut the threaded rod 1" less than the distance measured in step 1. This will give you the ability to adjust the linkage about 3/4" shorter than the distance you need, and up to 1 1/2" longer (the rod threads 1" deep into each Heim joint.) Dress the cut end of the threaded rod with a grinding wheel or file to prevent cross threading of the Heim joint.

Install the hex nuts (or jam nuts) and Heim joints onto each end of the threaded rod. Ensure the joints are threaded down completely. Cut the 5/16" steel brake line to match the distance from jam nut to jam nut. Remove one end of the Heim joints and jam nuts and slide the brake line over the threaded rod.

While the brake line is not necessary, it adds a nice touch. It can be polished up with steel wool, left plain, or painted to taste. Either way the end result is a heavy-duty throttle linkage that functions as well as it looks. It's a wonder why anyone would put up with the factory accelerator rod.

The new linkage is intended to mount in the 1/2" upper hole on Holley carburetor throttle arms. A bushing must be used to reduce this hole. The chrome stepped bushings in this photo are available from Moroso and others for about $5. However in a pinch these rubber insulated washers work nicely, and are available for pennies at the hardware store (usually on self tapping metal screws as seen here.)

The above mentioned reducer bushings fit into the Holley throttle arm as shown. Use one on each side. Alternatively the insulated washers work well. Use one on either side with the rubber end facing inside the hole. The attaching point at the pedal arm on many early Fords is also 1/2" (with factory plastic bushing removed.) The insulated washers work fine here as well. Use the Allen head screws and nylon-insert lock nuts to secure the rod ends to the mounting points.

The easiest way to determine proper throttle linkage length is to set it to manually open the throttle blades completely. Have some one press the accelerator pedal to the floor. Now adjust the rod ends to the line up with the distance between the upper mounting hole in the throttle arm and the mounting hole in the pedal arm.

Mounting to the upper hole in the Holley arm upward creates a slight angle on the throttle linkage, giving it leverage to pull the throttle arm over center and ensure complete opening of the throttle blades. The spherical rod bearings prevent binding are allow the rod to be fastened securely. Always use two return springs, ideally pulling in opposite directions to prevent a stuck throttle.